1. Field of the Invention
This invention relates to an apparatus for coating the inside of pipes, in particular the coolant pipes of steam condensers and heat exchangers with plastic mixtures.
2. Description of Related Art Including Information Disclosed under 37 CFR 197 and 1.98
It is known to provide steam condensers, as are used for example in plants for producing electric energy, with a plastic coating to counteract corrosion signs, in particular erosion. Pipe bottoms and the coolant pipes issuing therefrom are exposed to a great number of external influences, in particular mechanical, chemical and electromechanical stresses.
Mechanical stresses result from solid particles, for example sand, entrained by the coolant. Furthermore, the temperature difference between the cooling medium and the steam to be condensed, which can exceed 100.degree. C., causes expansion which leads to mechanical stress in particular in the roll-in area of the coolant pipes.
Chemical stresses result from the nature of the cooling medium, for example its load of salts, basic or acidic substances. One might mention in particular the known corrosion effect of sea water used for cooling purposes or heavily polluted river water.
Electrochemical or galvanic corrosion involves that which occurs through the formation of galvanic elements on metallic boundary surfaces, in particular at the transitions from pipe bottom to coolant pipe, and which is greatly promoted by electroconductive liquids, e.g. sea water.
Moreover, the operability of steam condensers is impaired by the deposition of undesirable substances, alga formation, etc., which is promoted in particular by roughness as arises through corrosion signs. This means that corrosion and deposition signs speed up as the service life of a steam condenser increases, because more and more starting points for corrosion and deposits form.
One therefore began early to provide steam condensers with an anticorrosive coating of plastic materials. One uses in particular thick coatings of epoxy resin.
At first only the pipe bottoms themselves were mainly coated, which does not solve the special problems involved in the formation of corrosion signs and deposits in the pipes. Later the pipe inlets and outlets were also included in the coating to protect the especially endangered transitional area. Measures of the abovementioned type are known for example from GB-A-1 125 157, DE-U-1 939 665, DE-U-7 702 562, EP-A-0 236 388 and EP-A-94 106 304.
However it has turned out that only complete coating of the coolant pipes as well can ensure long-lasting corrosion prevention and a long service life. Coating the inside of such coolant pipes is a great problem, however, because of their sometimes considerable length and their small diameter, in particular considering that the coating must be extremely uniform in order to create few starting points for deposits and corrosion signs. At the same time it must be possible to provide the coating in situ and in a very short time in order to minimize the plant down-time. In view of the great number of coolant pipes in steam condensers, which include several thousand pipes, this means that the coating method must be largely automated and standardized.